The advent of mobile computing devices such as smart phones and tablet computers has enabled users to perform computing functions away from their desks and offices. Users operate mobile computing devices while they are walking, driving, etc. However, traditional mobile computing devices employ a fixed display and touch screen command interface. Operating these mobile computing devices while moving can create a dangerous situation as the users hands and eyes should be focused on their mobility task (e.g., walking or driving), rather than operating their mobile computing device.
To reduce the risks associated with operating a mobile computing device while moving, hands-free command interfaces based on voice recognition have been developed. Voice recognition allows the user to operate the mobile computing device while their hands and eyes are focused on more important tasks. However, compared to standard point-and-click operation, voice recognition is slow, unreliable, and limited to a simple, lengthy string of questions. If the user has to listen to a string of selection choices and then speak to the machine, the interface often frustrates the user and is left unused.
Alternative hands-free command interfaces based on tracking eye movement have been explored. Human eyes can move much faster than hands. As a method of pointing, eyes work much faster than a computer mouse, and many orders-of-magnitude faster than voice recognition. However, it is recognized that while eyes can move quickly, the movements are often spontaneous and even erratic. Therefore, eye movements alone are not a reliable command input.
Nonaka introduces an interface to a fixed computer system that combines the simultaneous tracking of the direction of gaze and head gesture as a command input. Additional details are presented in “Communication Interface with Eye-Gaze and Head Gesture Using Successive DP Matching and Fuzzy Inference,” by Hidetoshi Nonaka, Journal of Intelligent Information Systems, 21:2, 105-112, 2003, the content of which is incorporated herein by reference in its entirety. The display of the computing system subject to control is fixed in the environment. To resolve a fixed gaze point, the system simultaneously tracks both eye and head movement to identify whether the head and eye movements are coordinated by the vestibulo-ocular reflex (VOR). If VOR is detected, the assumption is that the gaze is fixed and the head gesture is deliberate. In other words, evidence that the user is engaged in a VOR is used as an indicator of a human decision. Although this approach is suitable when the display of the computing system is fixed in the environment, it is unworkable when the display of the computing system subject to control is wearable.
In wearable display systems, a fixed gaze line indicates focus on an object in the environment, rather than an image projected by the display. Thus, detecting the VOR reflex during head movement cannot serve as an effective interface between the user and the wearable display system. Thus, improvements in the interface between a wearable computing system and its user are desired.